Re: [PATCH v3 3/4] nvdimm acpi: introduce _FIT

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 2 Nov 2016 23:40:56 +0800
Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:

> On 11/02/2016 12:24 AM, Igor Mammedov wrote:
> > On Sat, 29 Oct 2016 00:35:39 +0800
> > Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:
> >  
> >> _FIT is required for hotplug support, guest will inquire the updated
> >> device info from it if a hotplug event is received
> >>
> >> As FIT buffer is not completely mapped into guest address space, so a
> >> new function, Read FIT whose UUID is UUID
> >> 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62, handle 0x10000, function index
> >> is 0x1, is reserved by QEMU to read the piece of FIT buffer. The buffer
> >> is concatenated before _FIT return
> >>
> >> Refer to docs/specs/acpi-nvdimm.txt for detailed design
> >>
> >> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> >> ---
> >>  docs/specs/acpi_nvdimm.txt |  58 ++++++++++++-
> >>  hw/acpi/nvdimm.c           | 204 ++++++++++++++++++++++++++++++++++++++++++++-
> >>  2 files changed, 257 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/docs/specs/acpi_nvdimm.txt b/docs/specs/acpi_nvdimm.txt
> >> index 0fdd251..4aa5e3d 100644
> >> --- a/docs/specs/acpi_nvdimm.txt
> >> +++ b/docs/specs/acpi_nvdimm.txt
> >> @@ -127,6 +127,58 @@ _DSM process diagram:
> >>   | result from the page     |      |              |
> >>   +--------------------------+      +--------------+
> >>
> >> - _FIT implementation
> >> - -------------------
> >> - TODO (will fill it when nvdimm hotplug is introduced)
> >> +Device Handle Reservation
> >> +-------------------------
> >> +As we mentioned above, byte 0 ~ byte 3 in the DSM memory save NVDIMM device
> >> +handle. The handle is completely QEMU internal thing, the values in range
> >> +[0, 0xFFFF] indicate nvdimm device (O means nvdimm root device named NVDR),
> >> +other values are reserved by other purpose.
> >> +
> >> +Current reserved handle:
> >> +0x10000 is reserved for QEMU internal DSM function called on the root
> >> +device.  
> > Above part should go to section where 'handle' is defined, i.e. earlier in the file:
> >
> >    ACPI writes _DSM Input Data (based on the offset in the page):
> >    [0x0 - 0x3]: 4 bytes, NVDIMM Device Handle, 0 is reserved for NVDIMM
> >                 Root device.
> >  
> 
> Okay.
> 
> >  
> >> +QEMU internal use only _DSM function
> >> +------------------------------------
> >> +UUID, 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62, is reserved for QEMU internal
> >> +DSM function.
> >> +
> >> +There is the function introduced by QEMU and only used by QEMU internal.
> >> +
> >> +1) Read FIT  
> > UUID 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62 is reserved for Read_FIT DSM function
> > (private QEMU function)
> >  
> 
> okay.
> 
> >> +   As we only reserved one page for NVDIMM ACPI it is impossible to map the
> >> +   whole FIT data to guest's address space. This function is used by _FIT
> >> +   method to read a piece of FIT data from QEMU.  
> >  _FIT method uses Read_FIT function to fetch NFIT structures blob from QEMU
> >  in 1 page sized increments which are then concatenated and returned as _FIT method result.
> >  
> 
> okay.
> 
> >  
> >> +
> >> +   Input parameters:
> >> +   Arg0 – UUID {set to 648B9CF2-CDA1-4312-8AD9-49C4AF32BD62}
> >> +   Arg1 – Revision ID (set to 1)
> >> +   Arg2 - Function Index, 0x1
> >> +   Arg3 - A package containing a buffer whose layout is as follows:
> >> +
> >> +   +----------+-------------+-------------+-----------------------------------+
> >> +   |  Filed   | Byte Length | Byte Offset | Description                       |  
> >          ^ field,   s/Byte//,    s/Byte//  
> >> +   +----------+-------------+-------------+-----------------------------------+
> >> +   | offset   |     4       |    0        | the offset of FIT buffer          |  
> > offset in QEMU's NFIT structures blob to read from  
> 
> okay.
> 
> >  
> >> +   +----------+-------------+-------------+-----------------------------------+
> >> +
> >> +   Output:
> >> +   +----------+-------------+-------------+-----------------------------------+
> >> +   |  Filed   | Byte Length | Byte Offset | Description                       |
> >> +   +----------+-------------+-------------+-----------------------------------+
> >> +   |          |             |             | return status codes               |
> >> +   |          |             |             |   0x100 indicates fit has been    |
> >> +   | status   |     4       |    0        |   updated                         |  
> > 0x100 - error caused by NFIT update while read by _FIT wasn't completed  
> 
> okay.
> 
> >  
> >> +   |          |             |             | other follows Chapter 3 in DSM    |  
> > s/other follows/other codes follow/  
> 
> okay.
> 
> >  
> >> +   |          |             |             | Spec Rev1                         |
> >> +   +----------+-------------+-------------+-----------------------------------+
> >> +   | fit data |  Varies     |    4        | FIT data                          |
> >> +   |          |             |             |                                   |
> >> +   +----------+-------------+-------------+-----------------------------------+  
> > what does "Varies" mean, how would I know reading this how much data Read_FIT should read
> > from shared page?  
> 
> I mean other bytes in the buffer returned by this function except the 'status' field
> will be used as fit data. Maybe it is has a 'length' field?
you fill in length in C and access it in AML code and it's a part of output buffer format
so document it properly here.

> 
> >  
> >> +
> >> +   The FIT offset is maintained by the caller itself,  
> > probably is not necessary sentence, or specify a caller (for example OSPM)
> >  
> 
> Okay.
> 
> >> current offset plugs  
> >                  ^^^^?  
> 
> Typo. should be plus.
> 
> >  
> >> +   the length returned by the function is the next offset we should read.
> >> +   When all the FIT data has been read out, zero length is returned.
> >> +
> >> +   If it returns 0x100, OSPM should restart to read FIT (read from offset 0
> >> +   again).  
> > [...]
> > that's all for doc part, I'll do the code part later.
> >  
> 
> Thank you, Igor.
>